Tag Archives: PDF

Why does one PDF display and another one download?

Sometimes when you click on a link to a PDF, it comes up in the browser. Other times, the browser downloads the file. Everyone must wonder why, but few have wondered enough to find out. Here’s a quick explanation.

It has nothing to do with the PDF version, the content of the file, or the link. It’s the HTTP headers that make the difference. Specifically, a header called “Content-Disposition” is the determining factor. If it’s absent, the file will open in the browser. If it’s present, the value it specifies determines how you get the file.
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When sloppy redaction fails, resort to censorship

The Broward County School Board used an idiot’s form of “redaction” on a PDF before sending it to the media. The Sun Sentinel removed the blackout layer from the file and found newsworthy information on shooter Nikolas Cruz. They published it. Judge Elizabeth Scherer flew into a rage. She decreed, “From now on if I have to specifically write word for word exactly what you are and are not permitted to print… then I’ll do that.”

That’s called prior restraint, or censorship.
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PDF or HTML for public documents?

Should official online documents be PDF files? Many institutions say they obviously should, but the format has some clear disadvantages. An article on the UK’s Government Digital Service site argues that HTML, not PDF, is the right format for UK government documents. Its arguments, to the extent that they’re valid, apply to lots of other documents.

It makes a plausible case against PDF. The trouble is that the case against HTML is even stronger in some ways.
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PDF in three dimensions

There are two ways to put 3D models into a PDF file. Neither of them is an extension of the two-dimensional PDF model. Rather, they’re technologies which were developed independently, which can be wrapped into a PDF, and which software such as Adobe Acrobat can work with.

PDF has become a container format as much as a representational format. It can hold anything, and some of the things it holds have more or less official status, but there are no common architectural principles. The two formats used with PDF are U3D and PRC. Both are actually independent file formats which a PDF can embed.
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PDF/L?

Here’s a question for the gallery: Have any of you heard of PDF/L, and do you know what it is?
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File corruption and political corruption

When people who don’t understand file formats manipulate files in order to cover their tracks, they generally fail miserably. Slate magazine gives an entertaining case in point from the Trump scandals. The article says:

There are two types of people in this world: those who know how to convert PDFs into Word documents and those who are indicted for money laundering. Former Trump campaign chairman Paul Manafort is the second kind of person.

The PDF Association chimes in with additional technical details.
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JHOVE webinar

An Open Preservation Foundation webinar, “Putting JHOVE to the acid test: A PDF test-set for well-formedness validation in JHOVE,” will be held on November 21, 10 AM GMT (that’s 11 AM in Central Europe and a ludicrous 5 AM or earlier in the US).
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The PDF/A controversy

Is PDF/A a good archival format? Many institutions use it, but it has problems which are inherent in PDF. With PDF/A-3, it has lost some of its focus. A format which can be a container for any kind of content isn’t great for digital preservation.

An article by Marco Klindt of the Zuse Institute Berlin takes a strong position against its suitability, with the title “PDF/A considered harmful for digital preservation.” Carl Wilson at the Open Preservation Foundation has added his own thoughts with “PDF/A and Long Term Preservation.”

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PDF 2.0

The ISO specification for PDF 2.0 is now out. It’s known as ISO 32000-2. As usual for ISO, it costs an insane 198 Swiss francs, which is roughly the same amount in dollars. In the past, Adobe has made PDF specifications available for free on its own site, but I can’t find it on adobe.com. Its PDF reference page still covers only PDF 1.7.

ISO has to pay its bills somehow, but it’s not good if the standard is priced so high that only specialists can afford it. I don’t intend to spend $200 to be able to update JHOVE without pay. With some digging, I’ve found it in an incomplete, eyes-only format. All I can view is the table of contents. There are links to all sections, but they don’t work. I’m not sure whether it’s broken on my browser or by intention. In any case, it’s a big step backward as an open standard. I hope Adobe will eventually put the spec on its website.
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Figuring out the PDF version is harder than you think

In a GitHub comment, Johan van der Knijff noted how messy it is to determine the version of a PDF file. He looked at a file with the header characters “%PDF-1.8”. DROID says this isn’t a PDF file at all.

By a strict reading of the PDF specification, it isn’t. The version number has to be in the range 1.0 through 1.7. Being this strict seems like a bad idea, since it would mean format recognition software will fail to recognize any future versions of the format. (JHOVE doesn’t care what character comes after the period.)
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